Nagi Umino and Erika Amano, a studious high school student and a social media star, had nothing that linked them together—until they found out they were swapped at birth. When the sudden news is revealed to both of their families, their parents quickly devise a proposition with neither Nagi's nor Erika's knowledge: in order to restore them both to their rightful families and ensure everyone's happiness, the two should get engaged. When informed of this, Nagi and Erika are quick to reject the absurd plan, refusing to go along with their parents' wishes. But, with neither party willing to back down, only time can tell where their relationship will go.

Shigeru Akagi, a teenage mahjong genius, repeatedly defeats seasoned Jyanshis thanks to his bravery and drive. However, Shigeru’s fiercest nemesis, Iwao Washizu, enters the Mahjong Soul with enormous wealth and good fortune to resume his battle with Shigeru.

Special episode included in the Blu-ray Box of Ano Natsu de Matteru.

A special unaired episode included in the 7th DVD/Blu-ray volume.